One of the major problems with the application of nanotechnology is that the properties of the materials depend sensitively of the size of the particles. It is very difficult to grow particles or particle clusters that are relatively monodisperse (one size only). It is also very difficult to grow structures that have selected sizes over a wide size range using a single process.
For example, in the field of MRI (magnetic resonance imagining), it is known to grow nanoparticle clusters for the production of contrast agents by simultaneous in situ growth and stabilisation of the nanoparticles in the presence of polymers (usually dextran) or polyelectrolytes. Such techniques are described, for example, in WO2005076938 which provides a description of multi-polymer-coated magnetic nanoparticle clusters, aqueous magnetic fluids comprising same, and methods of their use in separation procedures. The multi-polymer-coated magnetic nanoparticle clusters comprise a super paramagnetic core, with a first polymer attached thereto, which does not render the first polymer-super paramagnetic particle complex colloidally stable, and a second polymer attached thereto, which stabilizes the complex. Methods of separation, including separation of expressed protein from cells and viruses expressing the same are all described. Although the described method has the ability to provide a stable cluster, the size control of the formed clusters is determined by the surface chemistry of the stabilising polymer used and the larger clusters are essentially polymers with low nanoparticle content. It is therefore difficult to control the size distribution of the formed clusters.
In summary, using such known techniques, the size of the cluster finally obtained is process controlled as opposed to user controlled. It can therefore be difficult to generate samples of reproducible size. Additionally, a broad range of cluster sizes is obtained
There is therefore a need for a methodology that will enable a production of nano-sized objects formed from different materials and of a controlled size.